Cancer is generally treated with surgery, chemotherapy, radiation therapy, or often a combination of approaches are taken. Radiation therapy (aka radiation oncology or radiotherapy), sometimes abbreviated to XRT, is the medical use of ionizing radiation, generally as part of cancer treatment to control or kill malignant cells. Historically, the three main divisions of radiation therapy are external beam radiation therapy, brachytherapy, and systemic radioisotope therapy. However, external beam radiotherapy is the most common form of radiotherapy and is popular because precise targeting of a tumor is possible.
In external beam radiotherapy, the patient sits or lies on a couch and an external source of radiation is pointed at a particular part of the body. Where the beams intersect, the radiation is highest, allowing the radiation oncologist to target the diseased tissue. Kilovoltage (“superficial”) X-rays are used for treating skin cancer and superficial structures. Megavoltage (“deep”) X-rays are used to treat deep-seated tumors (e.g. bladder, bowel, prostate, lung, or brain). While X-ray and electron beams are by far the most widely used sources for external beam radiotherapy, some centers employ heavier particle beams, particularly proton sources, although additional radiation sources are also possible.
Although a high level of targeting is possible, there is always some amount of radiation that passes through healthy tissue. Further, a margin of error is typically included in the treatment plan and allows a certain amount of external or internal movement, or the inevitable inaccuracies in patient positioning. Thus, a patient treated with external radiation therapy will have radiation damage due to the destruction of both healthy and cancerous tissues during external radiation treatment. Hence, it is always desirable to precisely position a patient and reduce both internal and external patient movement, thus reducing the margins and allowing for more precise targeting of the tumor.
Current methods of immobilizing patients use moldable cushions that are custom-made for each patient. These moldable cushions are a viable solution, but are less than ideal for a number of reasons. First, the cushions take up a large amount of physical space because the cushions are custom-made for each patient. Another problem with moldable cushions is that they are not effective in keeping the patient in a fixed position over multiple sessions, because the cushions allow a certain wiggle room. Thus, a patient may be in a slightly different position in one session than another, which can cause great difficulties in the treatment with external beam therapy.
Furthermore, such systems are static, and cannot be manipulated during therapy as the patients anatomy and/or position changes. The moldable cushions do not account for weight gain or loss between treatment sessions, nor do they accommodate the natural movements of respiration.
Thus, a need has arisen for a patient immobilizing apparatus that has the ability to fix a patient in the same location over multiple sessions of treatment regardless of weight changes or patient movement.
Various patents have issued relating to patient immobilizers. U.S. Pat. No. 5,832,550, for example, discloses a moldable vacuum cushion for positioning a patient during radiation therapy treatment that includes an indexing bar with indexing pins to allow the attached cushion to be quickly, easily, accurately, and repeatably indexed on a baseplate or treatment table. The indexing bar may be releasably mounted on a frame member fixed to the cushion or may be directly mounted on the cushion. This is a simple mechanical system, and does not allow automated movement compensation.
U.S. Pat. No. 7,216,385 discloses an inflatable cushion for use in a system and method in supporting the knees and legs of a person during surgery that includes an inflatable bladder. A bladder port communicates with a source of inflating fluid. The system includes the source of pressurized fluid and a valve assembly to switchably control the inflation and deflation of the bladder. The bladder may have a removable cover extending around the bladder, and the bladder may have side pleats to assist in expanding with the cover having corresponding accordion folds. The method involves placing a patient on a surgical table, decompressing the patient's spine to a flat back/drop knee position, interposing the bladder between the table and the patient's knees and advancing the knees to a full prone position by inflating the bladder. While a useful first step in designing a effective immobilizer, this device in not a full-body, dedicated immobilizer, and does not automatically detect and compensate for patent movement. In effect, it is little more than an inflatable pillow with foot operable valve actuators and having limited functionality.
U.S. Pat. No. 4,893,367 discloses a system of separately adjustable pillows that is characterized by separately inflatable and deflatable containers, which may be emptied or filled from a connected source with a pressurized fluid, via a manifold provided with valves for each container. However, as above, no automated inflation or motion compensation is possible, nor communication with treatment devices, and the device is no more than a collection of inflatable pillows.
U.S. Pat. No. 6,327,724 discloses an inflatable positioning device that includes a pump, a tube extending from the pump, a valve intermediate the length of the tube and a non-rectangular inflatable pillow connected to the end of the tube remote from the pump. The non-rectangular inflatable pillow is dimensioned for positioning portions of a patient's body during surgery. As above, no automated movement compensation is possible.
There are available on the market several systems that offer image guided radiation therapy. For example, the Trilogy® Stereotactic System combines an X-ray imager with an optical guidance system using infrared cameras and a “respiratory gating” technology that coordinates treatment with respiration, to compensate for tumor motion due to the patient's breathing. However, an ideal system would compensate for patient movements, by adapting to the changes in a patient position in a way as to reduce the amount of beam off time, thus allowing the treatment to be completed in a much shorter time.
As noted, none of the above described art provides a fully satisfactory solution to the patient immobilization problem, and there is room for considerable improvement in the art. The ideal system will allow automatic, precise compensation for both interfraction motion (changes in position caused by day-to day set-up conditions) and intrafraction motion (changes in position during a treatment session because of normal respiratory and organ motion).